The present invention generally relates to immunotherapeutic agents and vaccines against pathogenic organisms such as bacteria, protozoa, viruses and fungus. More specifically, unlike prior art vaccines and immunotherapeutic agents based upon pathogenic subunits or products which exhibit the greatest or most specific molecular immunogenicity, the present invention uses the most prevalent or majorly abundant immunogenic determinants released by a selected pathogen such as Mycobacterium tuberculosis to stimulate an effective immune response in mammalian hosts. Accordingly, the acquired immunity and immunotherapeutic activity produced through the present invention is directed to those antigenic markers which are displayed most often on infected host cells during the course of a pathogenic infection without particular regard to the relative or absolute immunogenicity of the administered compound.
It has long been recognized that parasitic microorganisms possess the ability to infect animals thereby causing disease and often the death of the host. Pathogenic agents have been a leading cause of death throughout history and continue to inflict immense suffering. Though the last hundred years have seen dramatic advances in the prevention and treatment of many infectious diseases, complicated host-parasite interactions still limit the universal effectiveness of therapeutic measures. Difficulties in countering the sophisticated invasive mechanisms displayed by many pathogenic vectors is evidenced by the resurgence of various diseases such as tuberculosis, as well as the appearance of numerous drug resistant strains of bacteria and viruses.
Among those pathogenic agents of major epidemiological concern, intracellular bacteria have proven to be particularly intractable in the face of therapeutic or prophylactic measures. Intracellular bacteria, including the genus Mycobacterium and the genus Legionella, complete all or part of their lifecycle within the cells of the infected host organism rather than extracellularly. Around the world, intracellular bacteria are responsible for millions of deaths each year and untold suffering. Tuberculosis, caused by Mycobacterium tuberculosis, is the leading cause of death from infectious disease worldwide, with 10 million new cases and 2.9 million deaths every year. In addition, intracellular bacteria are responsible for millions of cases of leprosy. Other debilitating diseases transmitted by intracellular agents include cutaneous and visceral leishmaniasis, American trypanosomiasis (Chagas disease), listeriosis, toxoplasmosis, histoplasmosis, trachoma, psittacosis, Q-fever, and Legionellosis including Legionnaires"" disease. At this time, relatively little can be done to prevent debilitating infections in susceptible individuals exposed to these organisms.
Due to this inability to effectively protect populations from tuberculosis and the inherent human morbidity and mortality caused by tuberculosis, this is one of the most important diseases confronting mankind. More specifically, human pulmonary tuberculosis primarily caused by M. tuberculosis is a major cause of death in developing countries. Capable of surviving inside, macrophages and monocytes, M. tuberculosis may produce a chronic intracellular infection. By concealing itself within the cells primarily responsible for the detection of foreign elements and subsequent activation of the immune system, M. tuberculosis is relatively successful in evading the normal defenses of the host organism. These same pathogenic characteristics have heretofore prevented the development of an effective immunotherapeutic agent or vaccine against tubercular infections. At the same time tubercle bacilli are relatively easy to culture and observe under laboratory conditions. Accordingly, M. tuberculosis is particularly well suited for demonstrating the principles and advantages of the present invention.
Those skilled in the art will appreciate that the following exemplary discussion of M. tuberculosis is in no way intended to limit the""scope of the present invention to the treatment of M. tuberculosis. Similarly, the teachings herein are not limited in any way to the treatment of tubercular infections. On the contrary, this invention may be used to advantageously provide safe and effective vaccines and immunotherapeutic agents against the immunogenic determinants of any pathogenic agent expressing extracellular products and thereby inhibit the infectious transmission of those organisms.
Currently it is believed that approximately half of the world""s population is infected by M. tuberculosis resulting in millions of cases of pulmonary tuberculosis annually. While this disease is a particularly acute health problem in the developing countries of Latin America, Africa, and Asia, it is also becoming more prevalent in the first world. In the United States specific populations are at increased risk, especially urban poor, immunocompromised individuals and immigrants from areas of high disease prevalence. Largely due to the AIDS epidemic the incidence of tuberculosis is presently increasing in developed countries, often in the form of multi-drug resistant M. tuberculosis. 
Recently, tuberculosis resistance to one or more drugs was reported in 36 of the 50 United States. In New York City, one-third of all cases tested in 1991 were resistant to one or more major drugs. Though non-resistant tuberculosis can be cured with a long course of antibiotics, the outlook regarding drug resistant strains is bleak. Patients infected with strains resistant to two or more major antibiotics have a fatality rate of around 50%. Accordingly, a safe and effective vaccine against such varieties of M. tuberculosis is sorely needed.
Initial infections of M. tuberculosis almost always occur through the inhalation of aerosolized particles as the pathogen can remain viable for weeks or months in moist or dry sputum. Although the primary site of the infection is in the lungs, the organism can also cause infection of the bones, spleen, meninges and skin. Depending on the virulence of the particular strain and the resistance of the host, the infection and corresponding damage to the tissue may be minor or extensive. In the case of humans, the initial infection is controlled in the majority of individuals exposed to virulent strains of the bacteria. The development of acquired immunity following the initial challenge reduces bacterial proliferation thereby allowing lesions to heal and leaving the subject largely asymptomatic but possibly contagious.
When M. tuberculosis is not controlled by the infected, subject it often results in the extensive degradation of lung tissue. In susceptible individuals lesions are usually formed in the lung as the tubercle bacilli reproduce within alveolar or pulmonary macrophages. As the organisms multiply, they may spread through the lymphatic system to distal lymph nodes and through the blood stream to the lung apices, bone marrow, kidney and meninges surrounding the brain. Primarily as the result of cell-mediated hypersensitivity responses, characteristic granulomatous lesions or tubercles are produced in proportion to the severity of the infection. These lesions consist of epithelioid cells bordered by monocytes, lymphocytes and fibroblasts. In most instances a lesion or tubercle eventually becomes necrotic and undergoes caseation.
While M. tuberculosis is a significant pathogen, other species of the genus Mycobacterium also cause disease in animals including man and are clearly within the scope of the present invention. For example, M. bovis is closely related to M. tuberculosis and is responsible for tubercular infections in domestic animals such as cattle, pigs, sheep, horses, dogs and cats. Further, M. bovis may infect humans via the intestinal tract, typically from the ingestion of raw milk. The localized intestinal infection eventually spreads to the respiratory tract and is followed shortly by the classic symptoms of tuberculosis. Another important pathogenic vector of the genus Mycobacterium is M. leprae which causes millions of cases of the ancient disease leprosy. Other species of this genus which cause disease in animals and man include M. kansasii, M. avium intracellulare, M. fortuitum, M. marinum, M. chelonei, and M. scrofulaceum. The pathogenic mycobacterial species frequently exhibit a high degree of homology in their respective DNA and corresponding protein sequences amd some species, such as M. tuberculosis and M. bovis are highly related.
For obvious practical and moral reasons, initial work, in humans to determine the efficacy of experimental compositions with regard to such afflictions is infeasible. Accordingly, in the early development of any drug or vaccine it is standard procedure to employ appropriate animal models for reasons of safety and expense. The success of implementing laboratory animal models is predicated on the understanding that immunodominant epitopes are frequently active in different host species. Thus, an immunogenic determinant in one species, for example a rodent or guinea pig, will generally be immunoreactive in a different species such as in humans. Only after the appropriate animal models are sufficiently developed will clinical trials in humans be carried out to further demonstrate the safety and efficacy of a vaccine in man.
With regard to alveolar or pulmonary infections by M. tuberculosis, the guinea pig model closely resembles the human pathology of the disease in many respects. Accordingly, it is well understood by those skilled in the art that it is appropriate to extrapolate the guinea pig model of this disease to humans and other mammals. As with humans, guinea pigs are susceptible to tubercular infection with low doses of the aerosolized human pathogen M. tuberculosis. Unlike humans where the initial infection is usually controlled, guinea pigs consistently develop disseminated disease upon exposure to the aerosolized pathogen, facilitating subsequent analysis. Further, both guinea pigs and humans display cutaneous delayed-type hypersensitivity reactions characterized by the development of a dense mononuclear cell induration or rigid area at the skin test site. Finally, the characteristic tubercular lesions of humans and guinea pigs exhibit similar morphology including the presence of Langhans giant cells. As guinea pigs are more susceptible to initial infection and progression of the disease than humans, any protection conferred in experiments using this animal model provides a strong indication that the same protective immunity may be generated in man or other less susceptible mammals. Accordingly, for purposes of explanation only and not for purposes of limitation, the present invention will be primarily demonstrated in the exemplary context of guinea pigs as the mammalian host. Those skilled in the art will appreciate that the present invention may be practiced with other mammalian hosts including humans and domesticated animals.
Any animal or human infected with a pathogenic vector and, in particular, an intracellular organism presents a difficult challenge to the host immune system. While many infectious agents may be effectively controlled by the humoral response and corresponding production of protective antibodies, these mechanisms are primarily effective only against those pathogens located in the body""s extracellular fluid. In particular, opsonizing antibodies bind to extracellular foreign agents thereby rendering them susceptible to phagocytosis and subsequent intracellular killing. Yet this is not the case for other pathogens. For example, previous studies have indicated that the humoral immune response does not appear to play a significant protective role against infections by intracellular bacteria such as M. tuberculosis. However, the present invention may generate a beneficial humoral response to the target pathogen and, as such, its effectiveness is not limited to any specific component of the stimulated immune response.
More specifically, antibody mediated defenses seemingly do not prevent the initial infection of intracellular pathogens and are ineffectual once the bacteria are sequestered within the cells of the host. As water soluble proteins, antibodies can permeate the extracellular fluid and blood, but have difficulty migrating across the lipid membranes of cells. Further, the production of opsonizing antibodies against bacterial surface structures may actually assist intracellular pathogens in entering the host cell. Accordingly, any effective prophylactic measure against intracellular agents, such as Mycobacterium, should incorporate an aggressive cell-mediated immune response component leading to the rapid proliferation of antigen specific lymphocytes which activate the compromised phagocytes or cytotoxically eliminate them. However, as will be discussed in detail below, inducing a cell-mediated immune response does not equal the induction of protective immunity. Though cell-mediated immunity may be a prerequisite to protective immunity, the production of vaccines in accordance with the teachings of the present invention requires animal based challenge studies.
This cell-mediated immune response generally involves two steps. The initial step, signaling that the cell is infected, is accomplished by special molecules (major histocompatibility or MHC molecules) which deliver pieces of the pathogen to the surface of the cell. These MHC molecules bind to small fragments of bacterial proteins which have been degraded within the infected cell and present them at the surface of the cell. Their presentation to T-cells stimulates the immune system of the host to eliminate the infected host cell or induces the host cell to eradicate any bacteria residing within.
Unlike most infectious bacteria Mycobacterium, including M. tuberculosis tend to proliferate in vacuoles which are substantially sealed off from the rest of the cell by a membrane. Phagocytes naturally form these protective vacuoles making them particularly susceptible to infection by this class of pathogen. In such vacuoles the bacteria are effectively protected from degradation, making it difficult for the immune system to present integral bacterial components on the surface of infected cells. However, the infected cell""s MHC molecules will move to the vacuole and collect any free (released) bacterial products or move to other sites in the host cell to which the foreign extracellular bacterial products have been transported for normal presentation of the products at the cell surface. As previously indicated, the presentation of the foreign bacterial products will provoke the proper response by the host immune system.
The problems intracellular pathogens pose for the immune system also constitute a special challenge to vaccine development. Thus far the production of an effective vaccine against Mycobacterium infections and, in particular, against M. tuberculosis has eluded most researchers. At the present time the only widely available vaccine against intracellular pathogens is the live attenuated vaccine BCG, an avirulent strain of M. bovis, which is used as a prophylactic measure against the tubercle bacillus. Yet in 1988, extensive World Health Organization studies from India determined that the efficacy of the best BCG vaccines was so slight as to be unmeasurable. Despite this questionable efficacy, BCG vaccine has been extensively employed in high incidence areas of tuberculosis throughout the world. Complicating the matter even further individuals who have been vaccinated with BCG will often develop sensitivity to tuberculin which negates the usefulness of the most common skin test for tuberculosis screening and control.
Another serious problem involving the use of a live, attenuated vaccine such as BCG is the possibility of initiating a life threatening disease in immunocompromised patients. These vaccines pose a particular risk for persons with depressed cell-mediated immunity because of their diminished capacity to fight a rapidly proliferating induced infection. Such individuals include those weakened by malnourishment and inferior living conditions, organ transplant recipients, and persons infected with HIV. In the case of BCG vaccine, high risk individuals also include those suffering from lung disorders such as emphysema, chronic bronchitis, pneumoconiosis, silicosis or previous tuberculosis. Accordingly, the use of attenuated vaccines is limited in the very population where they have the greatest potential benefit.
The use of live attenuated vaccines may also produce other undesirable side effects. Because live vaccines reproduce in the recipient, they provoke a broader range of antibodies and a less directed cell-mediated immune response than noninfectious vaccines. Often this shotgun approach tends to occlude the immune response directed at the molecular structures most involved in cellular prophylaxis. Moreover, the use of live vaccines with an intact membrane may induce opsonizing antibodies which prepare a foreign body for effective phagocytosis. Thus, upon host exposure to virulent strains of the target organism, the presence of such antibodies could actually enhance the uptake of non-attenuated pathogens into host cells where they can survive and multiply. Further, an attenuated vaccine contains thousands of different molecular species and consequently is more likely to contain a molecular species that is toxic or able to provoke an adverse immune response in the patient. Other problems with live vaccines include virulence reversion, natural spread to contacts, contaminating viruses and viral interference, and difficulty with standardization.
Similarly, noninfectious vaccines such as killed organisms or conventional second generation subunit vaccines directed at strongly antigenic membrane bound structures, are limited with respect to the inhibition of intracellular bacteria. Like attenuated vaccines, killed bacteria provoke an indiscriminate response which may inhibit the most effective prophylactic determinants. Further, killed vaccines still present large numbers of potentially antigenic structures to the immune system thereby increasing the likelihood of toxic reactions or opsonization by the immune system. Traditional subunit vaccines incorporating membrane bound structures, whether synthesized or purified, can also induce a strong opsonic effect facilitating the entry of the intracellular pathogen into phagocytes in which they multiply. By increasing the rate of bacterial inclusion, killed vaccines directed to intracellular surface antigens may increase the relative virulence of the pathogenic agent. Thus, conventional attenuated or killed vaccines directed against strongly antigenic bacterial surface components may be contraindicated in the case of intracellular pathogens.
In order to circumvent the problems associated with the use of traditional vaccines, developments have been made using extracellular proteins or their immunogenic analogs to stimulate protective immunity against specific intracellular pathogens. For example, this inventor""s U.S. Pat. No. 5,108,745, issued Apr. 28, 1992 discloses vaccines and methods of producing protective immunity against Legionella pneumophila and M. tuberculosis as well as other intracellular pathogens. These prior art vaccines are broadly based on extracellular products originally derived from proteinaceous compounds released extracellularly by the pathogenic bacteria into broth culture in vitro and released extracellularly by bacteria within infected host cells in vivo. As disclosed therein, these vaccines are selectively based on the identification of extracellular products or their analogs which stimulate a strong immune response against the target pathogen in a mammalian host.
More specifically, these prior art candidate extracellular proteins were screened by determining their ability to provoke either a strong lymphocyte proliferative response or a cutaneous delayed-type hypersensitivity response in mammals which were immune to the pathogen of interest. Though this disclosed method and associated vaccines avoid many of the drawbacks inherent in the use of traditional vaccines, conflicting immunoresponsive results due to cross-reactivity and host variation may complicate the selection of effective immunizing agents. Thus, while molecular immunogenicity is one indication of an effective vaccine, other factors may complicate its use in eliciting an effective immune response in vivo.
More importantly, it surprisingly was discovered that, particularly with respect to M. tuberculosis, conventional prior art methods for identifying effective protective immunity inducing vaccines were cumbersome and potentially ineffective. For example, SDS-PAGE analysis of bulk M. tuberculosis extracellular protein followed by conventional Western blot techniques aimed at identifying the most immunogenic of these extracellular components produced inconsistent results. Repeated testing failed to identify which extracellular product would produce the strongest immunogenic response and, consistent with prior art thinking, thereby function as the most effective vaccine. Many of the extracellular products of M. tuberculosis are well known in the art, having been identified and, in some cases, sequenced. Further, like any foreign protein, it can be shown that these known compounds induce an immune response. However, nothing in the art directly indicates that any of these known compounds will induce protective immunity as traditionally identified.
Accordingly, it is a principal object of the present invention to provide vaccines or immunotherapeutic agents and methods for their production and use in mounting an effective immune response against infectious bacterial pathogens which do not rely upon traditional vaccine considerations and selection techniques based upon highly specific, strongly immunogenic operability.
It is another object of the present invention to provide vaccines or immunotherapeutic agents and methods for their use to impart acquired immunity in a mammalian host against intracellular pathogens including M. tuberculosis, M. bovis, M. kansasii, M. avium-intracellulare, M. fortuitum, M. chelonei, M. marinum, M. scrofulaceum and M. leprae. 
It is an additional object of the present invention to provide easily produced vaccines and immunotherapeutic agents exhibiting reduced toxicity relative to killed or attenuated vaccines.
The present invention accomplishes the above-described and other objects by providing compounds for use as vaccines and/or immunotherapeutic agents and methods for their production to generate protective or therapeutic immune responses in mammalian hosts against infection by pathogens. In a broad aspect, the invention provides the means to induce a protective or therapeutic immune response against infectious vectors producing extracellular compounds. While the compounds of the present invention are particularly effective against pathogenic bacteria, they may be used to generate a protective or therapeutic immune response to any pathogen producing majorly abundant extracellular products.
For purposes of the present invention, the term xe2x80x9cmajorly abundantxe2x80x9d should be understood as a relative term identifying those extracellular products released in the greatest quantity by the pathogen of interest. For example, with respect to M. tuberculosis grown under various conditions of culture to an optical density of approximately 0.5, one skilled in the art should expect to obtain on the order of 10 xcexcg/L or more of a majorly abundant extracellular product. Thus, out of the total exemplary 4 mg/L total output of extracellular product for M. tuberculosis grown under normal or heat shock conditions, approximately fifteen to twenty (alone or in combination) of the one hundred or so known extracellular products will constitute approximately ninety percent of the total quantity. These are the majorly abundant extracellular products contemplated as being within the scope of the present invention and are readily identifiable as the broad bands appearing in SDS/PAGE gels. The remaining extracellular products are minor. Those skilled in the art will also appreciate that the relative quantitative abundance of specific major extracellular products may vary depending upon conditions of culture. However, in most cases, the identification of an individual majorly abundant extracellular product will not change.
Accordingly, the present invention may be used to protect a mammalian host against infection by viral, bacterial, fungal or protozoan pathogens. It should be noted that in some cases, such as in viral infections, the majorly abundant extracellular products may be generated by the infected host cell. While active against all microorganisms releasing majorly abundant extracellular products, the vaccines and methods of the present invention are particularly effective in generating protective immunity against intracellular pathogens, including various species and serogroups of the genus Mycobacterium. The vaccines of the present invention are also effective as immunotherapeutic agents for the treatment of existing disease conditions.
Surprisingly it has been found by this inventor that immunization with the most or majorly abundant products released extracellularly by bacterial pathogens or their immunogenic analogs can provoke an effective immune response irrespective of the absolute immunogenicity of the administered compound. Due to their release from the organism and hence their availability to host molecules involved in antigen processing and presentation and due to their naturally high concentration in tissue during infection, the majorly abundant extracellular products of a pathogenic agent are processed and presented to the host immune system more often than other bacterial components. In the case of intracellular pathogens, the majorly abundant extracellular products are the principal immunogenic determinants presented on the surface of the infected host cells and therefore exhibit a greater presence in the surrounding environment. Accordingly, acquired immunity against the majorly abundant extracellular products of a pathogenic organism allows the host defense system to swiftly detect pathogens sequestered inside host cells and effectively inhibit them.
More particularly, the principal or majorly abundant products released by pathogenic bacteria appear to be processed by phagocytes and other host immune system mechanisms at a greater rate than less prevalent or membrane bound pathogenic components regardless of their respective immunogenic activity or specificity. This immunoprocessing disparity is particularly significant when the pathogenic agent is an intracellular bacteria sequestered from normal immune activity. By virtue of their profuse and continual presentation to the infected host""s immune system, the most prevalent bacterial extracellular products or their immunogenic analogs provoke a vigorous immune response largely irrespective of their individual molecular immunogenic characteristics.
Majorly abundant extracellular products are the principal constituents of proteins and other molecular entities which are released by the target pathogen into the surrounding environment. Current research indicates that in some instances a single majorly abundant extracellular product may comprise up to 40% by weight of the products released by a microorganism. More often, individual majorly abundant extracellular products account for between from about 0.5% to about 25% of the total products released by the infectious pathogen. Moreover, the top five or six majorly abundant extracellular products may be found to comprise between 60% to 70% of the total mass released by a microorganism. Of course those skilled in the art will appreciate that the relative levels of extracellular products may fluctuate over time as can the absolute or relative quantity of products released. For example, pH, oxidants, osmolality, heat and other conditions of stress on the organism, stage of lifecycle, reproduction status and the composition of the surrounding environment may alter the composition and quantity of products released. Further, the absolute and relative levels of extracellular products may differ greatly from species to species and even between strains within a species.
In the case of intracellular pathogens extracellular products appear to expand the population of specifically immune lymphocytes capable of detecting and exerting an antimicrobial effect against macrophages containing live bacteria. Further, by virtue of their repeated display on the surface of infected cells, the majorly abundant or, principal extracellular products function as effective antigenic markers. Accordingly, pursuant to the teachings of the present invention, vaccination and the inducement of protective immunity directed to the majorly abundant extracellular products of a pathogenic bacteria or their immunogenically equivalent determinants, prompts the host immune system to mount a rapid and efficient immune response with a strong cell-mediated component when subsequently infected by the target pathogen.
In direct contrast to prior art immunization activities which have primarily been focused on the production of vaccines and the stimulation of immune responses based upon the highly specific molecular antigenicity of individual screened pathogen components, the present invention advantageously exploits the relative abundance of bacterial extracellular products or their immunogenic analogs (rather than their immunogenic specificities) to establish or induce protective immunity with compounds which may actually exhibit lower immunogenic specificity than less prevalent extracellular products. For the purposes of this disclosure an immunogenic analog is any molecule or compound sufficiently analogous to at least one majorly abundant extracellular product expressed by the target pathogen, or any fraction thereof, to have the capacity to stimulate a protective immune response in a mammalian host upon subsequent infection by the target pathogen. In short, the vaccines of the present invention are identified or produced by selecting the majorly abundant product or products released extracellularly by a specific pathogen (or molecular analogs capable of stimulating a substantially equivalent immune response) and isolating them in a relatively pure form. The desired prophylactic immune response to the target pathogen may then be elicited by formulating one or more of the isolated immunoreactive products using techniques well known in the art and immunizing a mammalian host prior to infection by the target pathogen.
It is anticipated that the present invention will consist of at least one, two or, possibly even several well defined immunogenic determinants. As a result, the present invention produces consistent, standardized vaccines which may be developed, tested and administered with relative ease and speed. Further, the use of a few well defined molecules corresponding to the majorly abundant secretory or extracellular products greatly reduces the risk of adverse side effects associated with conventional vaccines and eliminates the possible occlusion of effective immunogenic markers. Similarly, because the present invention is not an attenuated or a killed vaccine the risk of infection during production, purification or upon administration is effectively eliminated. As such, the vaccines of the present invention may be administered safely to immunocompromised individuals, including asymptomatic tuberculosis patients and those infected with HIV. Moreover, as the humoral immune response is directed exclusively to products released by the target pathogen there is little chance of generating a detrimental opsonic immune component. Accordingly, the present invention allows the stimulated humoral response to assist in the elimination of the target pathogen from antibody susceptible areas.
Another beneficial aspect of the present invention is the ease by which the vaccines may be harvested or produced and subsequently purified. For example, the predominantly abundant extracellular products may be obtained from cultures of the target pathogen, including M. tuberculosis or M. bovis, with little effort. As the desired compounds are released into the media during growth, they can readily be separated from the intrabacterial and membrane bound components of the target pathogen utilizing conventional techniques. More preferably, the desired immunoreactive constituents of the vaccines of the present invention may be produced and purified from genetically engineered organisms into which the genes expressing the specific extracellular products of M. tuberculosis, M. bovis, M. leprae or any other pathogen of interest have been cloned. As known in the art, such engineered organisms can be modified to produce higher levels of the selected extracellular products or modified immunogenic analogs. Alternatively, the immunoprotective products, portions thereof or analogs thereof, can be chemically synthesized using techniques well known in the art. Whatever production source is employed, the immunogenic components of the predominant or majorly abundant extracellular products may be separated and subsequently formulated into deliverable vaccines using common biochemical procedures such as fractionation, chromatography or other purification methodology and conventional formulation techniques.
For example, in an exemplary embodiment of the present invention the target pathogen is M. tuberculosis and the majorly abundant products released extracellularly by M. tuberculosis into broth culture are separated from other bacterial components and used to elicit an immune response in mammalian hosts. Individual proteins or groups of proteins are then utilized in animal based challenge experiments to identify those which induce protective immunity making them suitable for use as vaccines in accordance with the teachings of the present invention. More specifically, following the growth and harvesting of the bacteria, by virtue of their physical abundance the principal extracellular products are separated from intrabacterial and other components through centrifugation and filtration. If desired, the resultant bulk filtrate is then subjected to fractionation using ammonium sulfate precipitation with subsequent dialysis to give a mixture of extracellular products, commonly termed EP. Solubilized extracellular products in the dialyzed fractions are then purified to substantial homogeneity using suitable chromatographic techniques as known in the art and as described more fully below.
These exemplary procedures result in the production of fourteen individual proteinaceous major extracellular products of M. tuberculosis having molecular weights ranging from 110 kilo Daltons (KD) to 12 KD. Following purification each individual majorly abundant extracellular product exhibits one band corresponding to its respective molecular weight when subjected to polyacrylamide gel electrophoresis thereby allowing individual products or groups of products corresponding to the majorly abundant extracellular products to be identified and prepared for use as vaccines in accordance with the teachings of the present invention.
Subsequently, immunization and the stimulation of acquired immunity in a mammalian host system may be accomplished through the teachings of the present invention utilizing a series of subcutaneous or intradermal injections of these purified extracellular products over a course of time. For example, injection with a purified majorly abundant bacterial extracellular product in incomplete Freund""s adjuvant followed by a second injection in the same adjuvant approximately three weeks later can be used to elicit a protective response upon subsequent challenge with the virulent pathogen. Other exemplary immunization protocols within the scope and teachings of the present invention may include a series of three or four injections of purified extracellular product or products of their analogs in the adjuvant SAF over a period of time. While a series of injections may generally prove more efficacious, the single administration of a selected majorly abundant extracellular product or its immunogenic subunits or analogs can impart the desired immune response and is contemplated as being within the scope of the present invention as well.
Such exemplary protocols can be demonstrated using art accepted laboratory models such as guinea pigs. For example, as will be discussed in detail, immunization of several guinea pigs with a combination of five majorly abundant extracellular products (purified from M. tuberculosis as previously discussed) was accomplished with an immunization series of three injections of the bacterial products in SAF adjuvant with corresponding sham-immunization of control animals. Exemplary dosages of each protein ranged from 100 xcexcg to 2 xcexcg. Following the last vaccination all of the animals were simultaneously exposed to an infectious and potentially lethal dose of aerosolized M. tuberculosis and monitored for an extended period of time. The control animals showed a significant loss in weight when compared with the animals immunized with the combination of the majorly abundant extracellular products of M. tuberculosis. Moreover, half of the control animals died during the observation period while none of the immunized animals succumbed to tuberculosis. Autopsies conducted after this experiment revealed that the non-immunized control animals had significantly more colony forming units (CFU) and corresponding damage in their lungs and spleens than the protected animals.
It should be emphasized that the present invention is not restricted to combinations of secretory or extracellular products. For example, several alternative experimental protocols demonstrate the capacity of a single abundant extracellular product to induce mammalian protective immunity in accordance with the teachings of the present invention. In each experiment guinea pigs were immunized with a single majorly abundant extracellular product purified from M. tuberculosis EP using the chromatography protocols detailed herein. In one example the animals were vaccinated in multiple experiments with an adjuvant composition containing a purified abundant secretory product having a molecular weight corresponding to 30 KD. In another example of the present invention, different guinea pigs were vaccinated with an adjuvant composition containing an abundant extracellular product isolated from M. tuberculosis having a molecular weight corresponding to 71 KD. Following their respective immunizations both sets of animals and the appropriate controls were exposed to lethal doses of aerosolized M. tuberculosis to determine vaccine effectiveness.
More particularly, in one experiment six guinea pigs were immunized with 100 xcexcg of 30 KD protein in SAF on three occasions spread over a period of six weeks. Control animals were simultaneously vaccinated with corresponding amounts of a bulk preparation of extracellular proteins (EP) or buffer. Three weeks after the final vaccination, the animals were challenged with an aerosolized lethal dose of M. tuberculosis and monitored for a period of 14 weeks. The 30 KD immunized guinea pigs and those immunized with the bulk extracellular preparation had survival rates of 67% and 50% respectively (illustrating the unexpectedly superior performance of the majorly abundant extracellular product versus EP), while the sham-immunized animals had a survival rate of only 17%. Upon termination of the experiment the animals were sacrificed and examined for viable tubercle bacilli. Unsurprisingly, the non-immunized animal showed markedly higher concentrations of M. tuberculosis in the lungs and spleen.
Similar experiments were performed on those animals vaccinated with 71 KD protein. In one experiment six guinea pigs were vaccinated with an SAF adjuvant composition containing 100 xcexcg purified 71 KD protein two times over a period of three weeks. Other animals were similarly immunized with a bulk preparation of unpurified extracellular proteins or EP for use as a positive control and with buffer for use as a negative control. Following exposure to lethal doses of aerosolized tubercle bacilli the weight of the guinea pigs was monitored for a period of 6 months. Once again the animals immunized with the purified form of the abundant extracellular product developed protective immunity with respect to the virulent M. tuberculosis. By the end of that period the buffer immunized animals showed a significant loss in weight when compared with the immunized animals. Further, while the positive controls and 71 KD immunized animals had survival rates of 63% and 50% respectively, the non-immunized animals all died before the end of the observation period.
It is important to note that the formulation of the vaccine is not critical to the present invention and may be optimized to facilitate administration. Solutions of the purified immunogenic determinants derived from the majorly abundant pathogenic extracellular products may be administered alone or in combination in any manner designed to generate a protective immune response. The purified protein solutions may be delivered alone, or formulated with an adjuvant before being administered. Specific exemplary adjuvants used in the instant invention to enhance the activity of the selected immunogenic determinants are SAF, Freund""s incomplete adjuvant and Freund""s complete adjuvant containing killed bacteria. Additional adjuvants that may be useful in the present invention are water-in-oil emulsions, mineral salts (for example, alum), nucleic acids, block polymer surfactants, and microbial cell walls (peptido glycolipids). While not limiting the scope of the invention it is believed that adjuvants may magnify immune responses due to the slow release of antigens from the site of injection.